Two-Stroke Engines Flashcards

Why do two-stroke engines typically produce more emissions compared to four-stroke engines?

Answer: Two-stroke oil and loss of air-fuel mixture through the exhaust port

Explanation: Two-stroke engines produce more emissions primarily because they mix oil with the fuel, which burns and produces more pollutants. Additionally, the design of the engine leads to a loss of the air-fuel mixture through the exhaust port, contributing to unburned hydrocarbons and other emissions.

Why do two-stroke engines generally cost less to manufacture compared to four-stroke engines?

Answer: They have fewer parts

Explanation: Two-stroke engines cost less to manufacture primarily because they have a simpler design with fewer parts compared to four-stroke engines. This simplicity reduces the complexity of the manufacturing process, leading to lower production costs.

In what positions can a two-stroke leaf blower operate effectively?

Answer: Any position

Explanation: Two-stroke leaf blowers can operate effectively in any position due to their simple lubrication system, which does not rely on a sump and oil pump like four-stroke engines. This allows for flexibility in operation, making them suitable for various angles and orientations during use.

On a two-stroke engine, the crankshaft turns how many degrees to complete one full cycle:

Answer: 360 degrees

Explanation: In a two-stroke engine, the crankshaft completes one full cycle in 360 degrees of rotation. This means the engine completes all four stages of the combustion process (intake, compression, power, and exhaust) in just one crankshaft revolution, unlike a four-stroke engine which requires 720 degrees.

A two-stroke engine has a power stroke once _______.

Answer: every full revolution

Explanation: In a two-stroke engine, a power stroke occurs once every full revolution of the crankshaft. This contrasts with a four-stroke engine, which has a power stroke once every two revolutions of the crankshaft.

A two-stroke engine uses ________ fuel than a four-stroke engine.

Answer: more

Explanation: A two-stroke engine typically uses more fuel than a four-stroke engine because it completes a power cycle with every revolution, leading to higher fuel consumption. Additionally, some of the air-fuel mixture in a two-stroke engine can be lost through the exhaust port, further increasing fuel usage.

What purpose does the shape of a two-stroke piston serve?

Answer: Helps keep the air-fuel mixture from going straight out the exhaust and aids in expelling exhaust gases, a process called scavenging

Explanation: The shape of a two-stroke piston is designed to optimize the scavenging process, which involves directing the fresh air-fuel mixture to prevent it from escaping directly out of the exhaust port while also helping to expel the exhaust gases efficiently. This design enhances the engine's performance and efficiency.

Why is it not advisable to perform a leak-down test on a two-stroke engine?

Answer: You can damage the crank seals

Explanation: Performing a leak-down test on a two-stroke engine can potentially damage the crank seals. These seals are crucial for maintaining proper compression and preventing air or fuel leaks. Applying excessive pressure during the test can cause these seals to fail or become compromised, leading to issues with engine performance and reliability. Therefore, it is not recommended to conduct a leak-down test on a two-stroke engine.

What are the two benefits of a two-stroke engine design?

Answer: Lightweight and smaller size

Explanation: Two-stroke engines offer the benefits of lightweight construction and smaller size compared to their four-stroke counterparts. These characteristics make them desirable for applications where weight and space are significant considerations, such as handheld power tools, small recreational vehicles, and marine engines.

What are the two disadvantages of a two-stroke engine?

Answer: More noise and greater emissions

Explanation: Two-stroke engines are known for producing more noise and emitting greater levels of pollutants compared to four-stroke engines. These factors can be drawbacks in applications where noise pollution and environmental concerns are significant considerations.

What is the most common type of valve used in a two-stroke engine?

Answer: Reed valve

Explanation: The most common type of valve used in a two-stroke engine is the reed valve. Reed valves are thin, flexible plates typically made of metal or composite materials. They are positioned between the carburetor and the crankcase intake port and function to control the flow of air-fuel mixture into the engine. Reed valves are preferred in two-stroke engines due to their simplicity, reliability, and effectiveness in optimizing engine performance.